Bernstein L R
Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06030, USA.
J Neurosci Res. 2001 Dec 15;66(6):1035-46. doi: 10.1002/jnr.10103.
Differences in the time-of-arrival of sounds at the two ears, or interaural temporal disparities (ITDs), constitute one of the major binaural cues that underlie our ability to localize sounds in space. In addition, ITDs contribute to our ability to detect and to discriminate sounds, such as speech, in noisy environments. For low-frequency signals, ITDs are conveyed primarily by "cycle-by-cycle" disparities present in the fine-structure of the waveform. For high-frequency signals, ITDs are conveyed by disparities within the time-varying amplitude, or envelope, of the waveform. The results of laboratory studies conducted over the past few decades indicate that ITDs within the envelopes of high-frequency are less potent than those within the fine-structure of low-frequency stimuli. This is true for both measures of sensitivity to changes in ITD and for measures of the extent of the perceived lateral displacement of sounds containing ITDs. Colburn and Esquissaud (1976) hypothesized that it is differences in the specific aspects of the waveform that are coded neurally within each monaural (single ear) channel that account for the greater potency of ITDs at low frequencies rather than any differences in the more central binaural mechanisms that serve these different frequency regions. In this review, the results of new studies are reported that employed special high-frequency "transposed" stimuli that were designed to provide the high-frequency channels of the binaural processor with envelope-based information that mimics waveform-based information normally available only in low-frequency channels. The results demonstrate that these high-frequency transposed stimuli (1) yield sensitivity to ITDs that approaches, or is equivalent to, that obtained with "conventional" low-frequency stimuli and (2) yield large extents of laterality that are similar to those measured with conventional low-frequency stimuli. These findings suggest that by providing the high-frequency channels of the binaural processor with information that mimics that normally available only at low frequencies, the potency of ITDs in the two frequency regions can be made to be similar, if not identical. These outcomes provide strong support for Colburn and Esquissaud's (1976) hypothesis. The use of high-frequency transposed stimuli, in both behavioral and physiological investigations offers the promise of new and important insights into the nature of binaural processing.
声音到达双耳的时间差异，即双耳时间差（ITD），是我们在空间中定位声音能力的主要双耳线索之一。此外，ITD有助于我们在嘈杂环境中检测和辨别声音，如语音。对于低频信号，ITD主要通过波形精细结构中存在的“逐周期”差异来传递。对于高频信号，ITD通过波形随时间变化的幅度（即包络）内的差异来传递。过去几十年进行的实验室研究结果表明，高频包络内的ITD比低频刺激精细结构内的ITD效力更低。这在对ITD变化的敏感度测量以及对包含ITD的声音感知横向位移程度的测量中都是如此。科尔伯恩和埃斯基索德（1976年）推测，是每个单耳（单耳）通道中神经编码的波形特定方面的差异，导致低频时ITD的效力更大，而不是服务于这些不同频率区域的更中枢双耳机制存在任何差异。在这篇综述中，报告了新研究的结果，这些研究采用了特殊的高频“转换”刺激，旨在为双耳处理器的高频通道提供基于包络的信息，这种信息模仿了通常仅在低频通道中可用的基于波形的信息。结果表明，这些高频转换刺激（1）产生的对ITD的敏感度接近或等同于用“传统”低频刺激获得的敏感度，（2）产生的侧向性程度与用传统低频刺激测量的相似。这些发现表明，通过为双耳处理器的高频通道提供模仿通常仅在低频时可用的信息，可以使两个频率区域中ITD的效力相似，甚至相同。这些结果为科尔伯恩和埃斯基索德（1976年）的假设提供了有力支持。在行为和生理研究中使用高频转换刺激有望为双耳处理的本质带来新的重要见解。
